1. Field of the Invention
This invention relates to a developer supplying apparatus in an image forming apparatus using the electrostatic recording process or the electrophotographic process, and particularly to a developer supplying apparatus in an image forming apparatus such as a copier, a printer or a facsimile apparatus.
2. Related Background Art
In image forming apparatuses using the electrophotographic process according to the conventional art, and above all, image forming apparatuses for effecting chromatic color image formation, two-component development using a mixture of a nonmagnetic toner and a magnetic carrier as a developer is widely utilized.
The two-component development, as compared with the presently known other developing methods, has such merits as the stability of the quality of image and the durability of the apparatus while on the other hand, the deterioration of the developer due to long-period endurance, particularly the deterioration of the carrier, has been unavoidable and therefore, with the long-period use of the image forming apparatus, it is necessary to perform the work of interchanging the developer.
Several techniques for solving this problem are known. For example, a technique disclosed in Japanese Patent Publication (Koukoku) No. 2-21591 will hereinafter be described briefly.
That is, in a developing device for an electrophotographic copier, provision is made of agitating means for agitating a carrier and a toner, and a developing roll for supplying the developer agitated by the agitating means to a photosensitive member, and a carrier supplying device and a toner supplying device separate from or integral with each other are provided above the agitating means, and further a developer spillover portion is provided on the side wall of the housing of the developing device.
By thus providing the developer spillover portion, it is possible to supply a fresh developer little by little by the supplying apparatus and also discharge the developer from the developer spillover portion and therefore, the characteristic of the developer in the housing of the developing device can be maintained constant and as the result, the quality of copy images can also be maintained constant.
Also, according to such a technique, the old developer in the housing of the developing device is sequentially automatically discharged from the developer spillover portion and therefore, the cumbersome developer interchanging work, as in an apparatus not provided with the developer spillover portion, including detaching the developing device from the copier, taking out the old developer in the housing of the device, refilling the housing with a fresh developer, and thereafter mounting the developing device again becomes unnecessary and moreover, the scattering of the developer is prevented, and this is hygienic.
The deteriorated developer (carrier) is gradually replaced with fresh developer, whereby the apparent progress of deterioration of the carrier is stopped and as the whole of the developer, the characteristic (developing characteristic) is stabilized. Thereby, the cumbersome work of the interchange of the developer is made unnecessary and improvements in a maintenance property and usability can be achieved.
However, in the case of the image forming apparatus according to the conventional art as described above, the following problem has arisen.
In recent years, the market of full color copiers/printers has enlarged and various functions have been required, and in such situations, it has become a proposition to supply the market with image forming apparatuses capable of forming, for example, images of high quality stably for a long period.
In the above-described apparatus, however, the carrier which has just been supplied and is not yet deteriorated is also discharged with the old developer and therefore, with a long-period use, there is brought about a state in which the remarkably deteriorated carrier and the slightly deteriorated carrier are mixed with each other and thus, the apparent progress of deterioration of the carrier is stopped and as the whole of the developer, the characteristic is stabilized, but the level of stabilization becomes a level considerably aggravated as compared with that during the initial installation.
That is, in the image forming apparatus according to the conventional art, the cumbersome work for the interchange of the developer becomes unnecessary and maintenance property and usability are improved, but the stability of the characteristic of the developer has been one at a low level, and it has been impossible to form images of high quality for a long period.
It is an object of the present invention to provide an image forming apparatus in which an improvement in a maintenance property concerned with the interchange of a developer can be achieved and also, a deteriorated carrier can be selectively shifted from a developer bearing member to an image bearing member.
Further objects of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings.